In many applications, it is important to optimize the interplay of an engine and its associated transmission--for instance, to reduce fuel consumption in motor vehicles it will be necessary not only to improve engine control systems but also to adapt transmission ratios. To achieve this, automatic transmissions present themselves as a solution, with CVTs (continuously variable transmissions) in particular being increasingly used. This type of transmission allows continuous adaptation of transmission ratios by means of a transmission element (chain, band, belt, etc) located between the discs of two disc assemblies. By applying the same contact pressure values on these two disc assemblies--this corresponds to the so-called pretensioning force--the force level for this transmission element will be adjusted. Specifying different values for this contact pressure on the two disc assemblies will create an additional transport force component for moving this transmission element; by varying this contact pressure, and thus the transport force, the transmission ratio may be continuously varied in any number of steps.
However, the problem here is that, when the transmission element slides (i.e. when excessive slip occurs), disc assemblies and the transmission element may be damaged. To prevent the transmission element from sliding, therefore, a high pretensioning force is specified; but this reduces transmission efficiency on the one hand and its service life on the other.